Field of the Invention
The invention relates to a load cell input unit adapted to measure a load of a load cell.
Description of Related Art
FIG. 6 is a diagram illustrating a flow of measuring a load by a conventional measuring system including a load cell 10 and a load cell input unit 930. The load cell 10 is a sensor used for transforming a load of a measuring object into an electric signal. The electric signal (i.e. input signal) output by the load cell 10 is input to the load cell input unit 930. The load cell input unit 930 calculates a weight or pressure according to the input signal, and outputs an output signal containing information of the calculated value to a host equipment 100 (i.e. an external control device) through an Ethernet for control automation technology (EtherCAT) coupler.
FIG. 7 is a structural diagram of a conventional measuring system 900. As shown in FIG. 7, the load cell 10 of the measuring system 900 includes a Wheatstone bridge circuit containing a strain gauge RL1 and three resistors RL2-RL4. Alternatively, the load cell 10 may have two or four strain gauges. An input signal EXC+ and an input signal EXC− are input to the load cell 10 from the load cell input unit 930. A Voltage of the input signal EXC+ and the input signal EXC− input to the load cell 10 is divided by the resistors RL2-RL4 and the strain gauge RL1. By applying a load to the load cell 10, a resistance of the strain gauge RL1 changes, and divided voltages of the resistors RL2-RL4 and the strain gauge RL1 also change. As a result, voltages of an electric signal SIG+ and an electric signal SIG− output from two output terminals of the load cell 10 change.
As shown in FIG. 7, the load cell input unit 930 has an amplifying element 931 and a load measuring element 32. The input signals input to the load cell input unit 930 from the load cell 10 are first input to the amplifying element 931 of the load cell input unit 930. The amplifying element 931 amplifies the input signals. Then, the input signals are input to the load measuring element 32. The load measuring element 32 calculates a weight or pressure, etc. according to the input signals. The load cell input unit 930 outputs an output signal containing information of a measured value such as the weight or the pressure to the post-stage host equipment 100 (referring to FIG. 6).
As shown in FIG. 7, the load cell 10 and the load cell input unit 930 are connected through six load cell connection cables 40. Two input terminals of the load cell 10 are respectively connected with two load cell connection cables 40. Moreover, two output terminals of the load cell 10 are respectively connected with one load cell connection cable 40. The two load cell connection cables 40 connected to the two input terminals of the load cell 10 are used for inputting the input signal EXC+ and the input signal EXC− to the load cell 10. Through other two load cell connection cables 40 that are connected to the two input terminals of the load cell 10, an electric signal S+ and an electric signal S− are input to the load cell input unit 930. Moreover, through the two load cell connection cables 40 connected to the two output terminals of the load cell 10, the electric signal SIG+ and the electric signal SIG− are input to the load cell input unit 930. The load measuring element 32 of the load cell input unit 930 calculates the weight or pressure, etc. based on the electric signal SIG+, the electric signal SIG−, the electric signal S+ and the electric signal S−.